In an engine for vehicles, an oil pump (i.e., an oil supply system) delivering the hydraulic oil to be used for lubrication of the engine to each portion of the engine has a variable discharge volume structure variably adjusting discharging pressure in response to the rotation of the engine. The above mentioned oil supply system is shown in JPH08 (1996)-114186A and JP2598994Y.
For example, the oil supply system described in JPH08 (1996)-114186A is provided with an oil pump including the first outlet port and the second outlet port discharging the hydraulic oil in response to the rotation of the rotor and the hydraulic-oil-delivery passage delivering the hydraulic oil to the hydraulic-oil receiving unit. The oil supply system is further provided with the first oil passage delivering the hydraulic oil discharged out of the first outlet port to the hydraulic-oil-delivery passage, the second oil passage delivering the hydraulic oil discharged out of the second outlet port to the hydraulic-oil-delivery passage and the return oil passage returning the hydraulic oil discharged out of the second outlet port to the oil pump. Furthermore, the oil supply system includes a control valve including the valve operable in response to the hydraulic pressure of the hydraulic oil of the first oil passage.
When the hydraulic pressure of the first oil passage is lower than a predetermined value, this control valve delivers the hydraulic oil via both the first oil passage and the second oil passage to the hydraulic-oil-delivery passage (i.e., a first mode). When the hydraulic pressure of the first oil passage is higher than the predetermined value, the control valve prevents merging of the hydraulic oil flow in the first and the second oil passages and allows the hydraulic-oil in the first oil passage to be delivered to the hydraulic-oil-delivery passage, and forces the hydraulic oil in the second oil passage to be returned to the return oil passage (i.e., a second mode). Accordingly, the oil supply system is capable of switching from the first mode to the second mode or vice versa.
As shown in FIG. 9, while the rotational speed of the rotor in the engine is in a low speed area lower than a predetermined speed (N1) (i.e., when the hydraulic pressure of the first oil passage is lower than the predetermined value), the discharged amount of the hydraulic oil discharged out of the oil supply system has a characteristic similar to a dotted line “a”. In other words, a supply amount of the hydraulic oil delivered to the hydraulic-oil-delivery passage is a total amount of the discharging amount of the first outlet port (i.e., a main outlet port) and the discharging amount of the second outlet port (i.e., a sub-outlet port) (i.e., the first mode).
In a first medium speed area starting from a point “Y” exceeding the predetermined speed (N1), the valve slides within the control valve according to the increase of the hydraulic pressure in the first oil passage, and a passage for returning to the return oil passage is open for communication. A rate of the increase of the discharging amount relative to the increase of the rotational speed becomes smaller (see a solid line “Y-Z” shown in FIG. 9).
When the rotational speed of the rotor further increases and reaches at a point “Z” which is a second medium speed area, the valve further slides in the control valve to prevent merging of the hydraulic oil in the first oil passage and the second oil passage (i.e., the second mode). In this case, the discharging amount of the hydraulic oil discharged out of the oil supply system is on a chain line “b” in FIG. 9 which shows the discharging amount at the first outlet port. In a high-speed area, thereafter, the discharging amount has an approximately similar characteristic to the chain line “b”. That is, the supply amount of the hydraulic oil delivered to the hydraulic-oil-delivery passage becomes approximately equal to the discharging amount of the first outlet port.
In the first mode, even when the rotational speed of the rotor is low, the required hydraulic pressure delivered to the hydraulic-oil receiving unit is secured by merging of the hydraulic oil in the first oil passage and the hydraulic oil in the second oil passage.
On the other hand, when the discharging amount discharged out of the first outlet port increases in response to the increase of the rotational speed of the rotor and the required hydraulic pressure is secured by the first oil passage only, the first mode is shifted to the second mode wherein the extra hydraulic oil discharged out of the second outlet port in the second oil passage is returned to the inlet port side via the return oil passage. As mentioned above, if the extra hydraulic oil is returned to the return oil passage from the second oil passage without delivering to the hydraulic-oil-delivery passage, the extra hydraulic oil would not be affected by a large hydraulic pressure. Accordingly, when the required hydraulic pressure is secured by the first oil passage only, an additional work in the oil pump device can be reduced or avoided and the driving horsepower of the oil supply system can be reduced.
According to the oil supply system disclosed in JPH08 (1996)-114186A, when an oil temperature of the hydraulic oil raises e.g., up to 130 degrees Celsius by increasing of the rotational speed of the rotor after the engine has been started, viscosity of the hydraulic oil becomes less and the hydraulic oil can easily be supplied to the spaces between each portion in the hydraulic-oil receiving unit. This will cause the increase of so-called oil leakage.
As shown in FIG. 9, when the rotational speed of the rotor in the engine increases and reaches at a point “Z”, the discharging amount of the hydraulic oil discharged out of the oil supply system indicated by a solid line in FIG. 9 has an approximately similar characteristic performance to the chine line “b” showing the discharging amount of the first outlet port. The difference between the chine line “b” and the solid line arises due to the oil leakage.
That is, viscosity of the hydraulic oil becomes more less in response to further increase of the rotational speed of the rotor, and an oil leakage phenomenon may occur frequently. In order to prevent this, however, there is a problem that it is difficult to keep the required oil amount for keeping the hydraulic pressure for a jet for a piston and a crank journal in the hydraulic-oil receiving unit.
Especially, in the jet for the piston, when the rotor rotates at a high speed, it is required to supply much hydraulic oil to the piston immediately. For that purpose, when the rotor rotates at high speed, it is preferable that the required oil amount corresponds to the discharging amount of the hydraulic oil discharged out of the oil supply system i.e., the total discharging amount (shown by a dotted line “a” in FIG. 9) adding up the discharging amount of the first and second outlet ports.
A need exists for providing an improved oil supply system capable of securing sufficiently a required oil amount for delivering to the hydraulic-oil receiving unit to, even when the engine rotates at high speed.